1. Field of the Invention
The present invention relates to a process for producing a photoresist polymeric compound (polymeric compound for photoresists) which is used typically for the preparation of photoresist resin compositions which in turn are adopted typically to fine patterning (microlithography) of semiconductor devices; to a process for producing a photoresist resin composition using a photoresist polymeric compound produced by the process; and to a process for producing a semiconductor device using the photoresist resin composition produced by the process.
2. Description of the Related Art
Positive-working photoresists used in fabrication of semiconductor devices should simultaneously have different characteristic properties such as a property of becoming soluble in an alkali in an exposed portion irradiated with light, adhesion to silicon wafers, plasma-etching resistance, and transparency to the light used. The positive-working photoresists are generally each used as a solution containing a base polymer, a photosensitive acid generator, and some types of additives for controlling the characteristic properties. Independently, the wavelength of a lithographic light source for use in the fabrication of semiconductor devices has become shorter year by year, and ArF excimer laser with a wavelength of 193 nm is promising as a next-generation light source. As photoresist polymers for use in such ArF excimer laser exposure system, there have been proposed various polymers having repeating units containing a lactone skeleton that exhibit high adhesion to substrates, and repeating units containing an alicyclic hydrocarbon skeleton that exhibits high etching resistance.
These polymers are generally prepared by polymerizing a monomer mixture to give a reaction mixture and isolating the target polymers by subjecting the reaction mixture to a precipitation treatment. The polymers produced in this manner, however, contain impurities such as metal components and thereby do not exhibit desired properties as resists (such as sensitivity) when used as resin components for photoresist resin compositions. Among such impurities, metal components such as sodium and iron, when contained in the polymers; adversely affect the electrical properties typically of semiconductor devices. Additionally, the resulting polymers are resistant to dissolution in a solvent for resist, because the surfaces of polymer particles become hard and/or the polymer particles fuse with each other when the isolated polymers are dried.
Japanese Unexamined Patent Application Publication (JP-A) No. 2006-37117 discloses a process for producing a photoresist polymeric compound having a lower sodium content by subjecting a monomer mixture to dropping polymerization to give a polymer; and subjecting the polymer to an extraction treatment with an organic solvent and water or passing a solution containing the polymer through a filter including a porous polyolefin membrane having a cation-exchange group, in which the monomer mixture contains at least one monomer selected from a monomer having a lactone skeleton, a monomer having a group capable of leaving with an acid to allow the polymeric compound to be soluble in an alkali, and a monomer having a hydroxyl-containing alicyclic skeleton. Even this process, however, does not always give a polymer sufficiently reduced in iron content, and the resulting polymeric compound may cause semiconductor devices to have deteriorated electrical properties.